Mile-wide tornado smashes Windsor, Colorado; plus, hurricane season commentary

By: Dr. Jeff Masters , 1:23 PM GMT on May 23, 2008

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A mile-wide tornado swept through Colorado between 11am and noon yesterday, ripping the roofs off buildings, tossing cars into the air, and killing at least one person in Weld County, northeast of Denver. Hail up to 2.75" in diameter accompanied the storm, which took an unusual north-northwesterly track , parallel to the Rocky Mountains north of Denver. Hardest hit was the town of Windsor, between Fort Collins and Greely, where damage appeared to be at least EF3. A local TV station took some impressive live video of the tornado, and a wunderground web cam video in Windsor, Colorado (Figure 1) caught the funnel as it passed east of the camera.


Figure 1.Webcam view looking east at 11:45am MDT in Windsor, Colorado as the tornado passed by. Note the golf ball-sized hail covering the ground. Image credit: windsorweather.com.

The Weather Underground's tornado expert, Rob Carver, had this explanation of yesterday's tornadoes:

Two low pressure systems over the Western U.S. were the cause of the severe weather outbreak of May 22. A strong upper-level low over the Great Basin formed a surface low in the lee of the Rockies, and brought a strong southerly mid-level jet over the Plains of Colorado and Kansas. As the surface low formed, it brought warm moist air northwards, forming a warm front. This warm air moved westward, rising with the terrain, causing thunderstorms to form. Once these storms formed, the juxtaposition of easterly flow at the surface with southerly flow aloft (i.e., wind shear) produced significant spin in the horizontal direction, which was tilted by the storms to vertical spin, which triggered the formation of tornadic thunderstorms. This movement of the warm front up the slope of the Rockies to help trigger tornadic thunderstorms is a rare occurrence.



Figure 2. Radar reflectivity image (top) of the Windsor, Colorado tornado at 11:45am MDT May 22, 2008. Note the classic hook-shaped echo associated with the tornado. Bottom: Doppler velocity image of the tornado, showing a small core of red and blue colors right next to each other, denoting strong winds towards and away from the radar, the classic signature of a tornado vortex. For those interested, we've saved an animation of the reflectivity and Doppler velocity.

Severe weather forecast
Severe weather is expected today over Kansas, Nebraska, and surrounding states. NOAA's Storm Prediction Center has placed portions of this area under its "Moderate Risk" category for severe weather, one step below its highest level of concern, "High Risk". Yesterday was also a "Moderate Risk" day, which SPC later upgraded to "High Risk" once the tornadoes started pounding Colorado. More severe weather is expected Saturday and Sunday over the Midwest as the upper-level low pressure system responsible moves slowly eastward. The Weather Underground Severe Weather page and Tornado page and WebCam page are good places to go to follow the severe weather. Also, tune in to the chase accounts and awesome storm photos from Wunderblogger Mike Theiss, who was in Kansas yesterday, and has posted many spectacular photos of yesterday's storms. According to Mike's blog:

Today Cloud 9 Tours saw 4 tornadoes and ONE developing almost overhead. We experienced winds over 100mph from the circulation of the meso that passed overhead as a cone tornado developed. Stay Tuned....


Possible development in the Eastern Pacific late next week
The past four days, the ECMWF model has been predicting the formation of a tropical storm in the the Eastern Pacific, just off the coast of Guatemala, around May 29. The GFS model has also been predicting something might develop, but in the Western Caribbean near Mexico's Yucatan Peninsula. The GFS has been rather inconsistent with its handling of this potential storm, and I am inclined to discount its forecast--especially since last night's long range runs of the NOGAPS, Canadian, and UKMET models all show development in the Eastern Pacific, not the Caribbean. All five models predict a northward shift in the jet stream and substantial relaxation in wind shear over the Eastern Pacific and Western Caribbean next week. It is common to see May tropical storms in the Eastern Pacific, and it would not be a surprise to see something develop there. I'd put the odds of something popping up in the Western Caribbean or Gulf of Mexico at less than 10%, though.

NOAA's seasonal hurricane forecast
NOAA issued its annual seasonal hurricane forecast yesterday, which I discussed in detail in yesterday's blog entry. Yesterday's forecast came out with a little more uncertainty attached to it than previous forecasts, which is a good thing. The media attention and fanfare that accompanies these forecasts is rather excessive, given the low skill they have. In fact, we don't even know if the NOAA forecasts have ANY mathematical skill, because they've never released a verification study of their forecasts. I doubt that the skill is very high--as Eric Berger of the Houston Chronicle pointed out in a blog yesterday, NOAA has blown its forecast of Accumulated Cyclone Energy (ACE) each of the last six years. NOAA held its usual press conference to announce the forecast; this year, it was held at the home of the NOAA Hurricane Hunter aircraft, MacDill AFB in Tampa. The NOAA dignitaries present said all the right things, preaching the need for preparedness regardless of the forecast for the upcoming hurricane season. Still, I wonder if NOAA might be hurting themselves by making such a public spectacle over the release of a forecast that no one knows the accuracy of, and has performed poorly by some measures in recent years. I do like the fact they are issuing public hurricane forecasts, as I expect their accuracy and value will improve in coming years, but they're definitely not worth the attention they're getting at present.

Jeff Masters

Tornado1 (kd7tda)
One of several tornados. This one was near Grainfield, KS
Tornado1
Tornado Damage 3 (jlg)
Damage from today's Tornado in Windsor, Colorado
Tornado Damage 3
()
Mean Looking Meso with Cone Tornado (MikeTheiss)
Photo os a wallcloud with a developing tornado passing just to the north of our location on May 22nd, 2008. Photo copyright Mike Theiss
Mean Looking Meso with Cone Tornado

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1657. Weather456
12:33 PM AST on May 25, 2008
oh I guess u guys saw it already
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1656. Weather456
12:29 PM AST on May 25, 2008
Also, if one was to go the NASA site, go to Goes-East visible imagery, medium zoom and lick a few degrees west of Costa Rico, there is a circulation. ASCAT should cross the area in the next hr or two. So I'm hoping for a good shot. But then again QuikSCAT across around 12Z this morning and revealed little so it maybe a mid-lower level spin.
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1654. Drakoen
4:29 PM GMT on May 25, 2008
1649. Weather456 4:29 PM GMT on May 25, 2008
I tried to create a balance between the numerical models and the current observations and it seems as though the intial disturbance will occur in the EPAC and moves northward due to the weaken westerly flow and more southerly flow. It would most likely emerge in the NW Caribbean, or the Yucatan Peninsula and as Drak pointed out it may turn west into the BOC. This seems to be the most likely scenario.

Another question:

How much will it develop on either side?


Most likely be weaker on the EPAC side and strengthen in the Caribbean. However, i'm watching this shortwave trough over the central Plains to see if it has any effect on the ridge.
Member Since: October 28, 2006 Posts: 57 Comments: 30213
1653. catastropheadjuster
4:23 PM GMT on May 25, 2008
To get in Vort's blog click on last comment. And he just can't keep it up while he's gone. Last night he said he would be back in about a week. I forget where he said they where going. But everyone can still get in there with no problem.He keeps a good blog with all the warnings up where folks can go and find out things. Rays,Aquak,MLC,Ally, and many others go there and help with keeping it up to date.
Sheri
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1652. weathersp
12:24 PM EDT on May 25, 2008
That track might that the GFS is showing might be possible...

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1651. Stormchaser2007
12:27 PM EDT on May 25, 2008
Well if it were to happen then it would have little TCHP to work with based on the course the GFS takes it.

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1650. cchsweatherman
12:24 PM EDT on May 25, 2008
Seems like most computer models agree on developing an Eastern Pacific storm, then crossing it over the middle Central America into the Northwest Caribbean through this week. This seems quite reasonable considering the forecasted MJO impulse which will induce a northerly shift in the Panama Monsoon Axis. But, once it gets into the Northwest Caribbean, then things get quite interesting as it will depend entirely upon the Atlantic ridge.
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1649. Weather456
12:24 PM AST on May 25, 2008
I tried to create a balance between the numerical models and the current observations and it seems as though the intial disturbance will occur in the EPAC and moves northward due to the weaken westerly flow and more southerly flow. It would most likely emerge in the NW Caribbean, or the Yucatan Peninsula and as Drak pointed out it may turn west into the BOC. This seems to be the most likely scenario.

Another question:

How much will it develop on either side?
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1648. IKE
11:28 AM CDT on May 25, 2008
I wonder if it's that circulation/spin west of Costa Rica?
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1646. CaneAddict
4:23 PM GMT on May 25, 2008
May 29th is the landfall of my birthday :-)!
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1645. nash28
4:24 PM GMT on May 25, 2008
Ok gang, need to shove some bacon in my face then off to mow the front.

BBL.
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1644. Drakoen
4:23 PM GMT on May 25, 2008
The cross over occurs between 108hr and 120hr then possible strengthening in the Caribbean. 144hr Its just east of the Yucatan.
Member Since: October 28, 2006 Posts: 57 Comments: 30213
1643. Weather456
12:20 PM AST on May 25, 2008
Also the information on my blog is updated to reflect new observations.
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1642. nash28
4:23 PM GMT on May 25, 2008
Since the GFS has been bullish for over a week now on a CB Low, and the 144hr mark is within a week, I'll buy that solution.
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1641. cchsweatherman
12:18 PM EDT on May 25, 2008
Looks like the GFS now agrees with the NOGAPS model and crosses the Eastern Pacific storm into the Northwest Caribbean through Nicaragua and Honduras at 126 hours (or sometime late Friday into Saturday).
12UTC GFS 126 HRS.
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1640. nash28
4:23 PM GMT on May 25, 2008
Thanks Sheri!
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1639. nash28
4:22 PM GMT on May 25, 2008
144hr mark on 12z GFS. Does show crossing over from EPAC.
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1638. Stormchaser2007
12:21 PM EDT on May 25, 2008
At 144 hrs there appears to be an area off of Africa as well as the Carrib storm.
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1637. catastropheadjuster
4:08 PM GMT on May 25, 2008
Hey all Vort isn't banned he has to leave for a week to go somewhere and will be back. You can click on the minutes where someone has posted and it will put u in his blog. I had to figure that out last night.
Sheri
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1636. nash28
4:21 PM GMT on May 25, 2008
Yep. Just a quick post on that from me...

Back to the weather.
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1635. Drakoen
4:21 PM GMT on May 25, 2008
1628. IKE 4:15 PM GMT on May 25, 2008
I see a spin off of the west coast of the Yucatan and in the East PAC......west of Costa Rica...

"clash of the personalities"...LOL.....the blogs downfall........


Exactly what I was thinking lol!
Member Since: October 28, 2006 Posts: 57 Comments: 30213
1634. Drakoen
4:19 PM GMT on May 25, 2008
The 12z GFS shows the area of low pressure crossing over from the EPAC...
Member Since: October 28, 2006 Posts: 57 Comments: 30213
1633. Stormchaser2007
12:18 PM EDT on May 25, 2008
Thats nice, My dog used to be so lonely until I got a little puppy for him to play around with......now back to 456 with the weather.
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1632. Weather456
12:14 PM AST on May 25, 2008
Made some updates

Well the models are rather split on the situation with the possible development in the Eastern Pacific and Western Caribbean. The 00Z runs of the CMC and UKMET and the 06Z GFS all showed development taking place in the Eastern Pacific, and moving northward into Guatemala, Central America. On the other hand, the 00Z runs of the ECMWF, NOGAPS and the 06Z GFS all showed some development taking place in the Western Caribbean; moving from Honduras into the Northwest portion and into the Yucatan Peninsula. The general time frame of genesis is around the 28/29th. Based on this, we cannot answer many questions, like where will take place. So we have to rely on other tools to do this. This morning%u2019s infrared imagery showed much of the shower and thunderstorm activity lies in the Eastern Pacific and this is the area that most models agree on that the initial disturbance will originate. In addition, visible satellite animation showed broad cyclonic turning just off the West Coast of Central America.

What the latter models are hinting on is that, the westerly flow in the Eastern Pacific will be enough to cause the disturbed area to enter the Southern Caribbean, but this morning%u2019s satellite derived winds, ASCAT/WindSAT sea winds and surface observations all indicate this flow is weakening. Furthermore, genesis potential and climatology favors development in the Eastern Pacific. This is not to say, that development in the Western Caribbean Sea is impossible, as there continues to be a persistent low level trough/circulation over Panama along with the forecasted upward pulse in the MJO. Also with a weakened westerly flow, it is possible this system moves northward into Central America and emerge and strengthen in the Northwestern Caribbean and any one part of that track seems to be in agreement with most models. However, currently, the intial disturbance will most likely occur in the Eastern Pacific.
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1631. nash28
4:17 PM GMT on May 25, 2008
Hound. Peanut is a Harrier. That dog is a Walker Hound. They are almost identical to each other.
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1630. Stormchaser2007
12:16 PM EDT on May 25, 2008
Nash what kind of dog are you considering??
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1629. nash28
4:15 PM GMT on May 25, 2008
Ok, I know this is a weather blog, but I have to post this real quick...

We're considering getting Peanut a sibling.

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1628. IKE
11:13 AM CDT on May 25, 2008
I see a spin off of the west coast of the Yucatan and in the East PAC......west of Costa Rica...

"clash of the personalities"...LOL.....the blogs downfall........
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1627. KEEPEROFTHEGATE (Mod)
12:08 PM EDT on May 25, 2008
there was a hissy fit in here last night thats about all it is
clash of the personalities
he deleted his blog and they have been posting in a old one since nash28
Member Since: July 15, 2006 Posts: 170 Comments: 53553
1626. Stormchaser2007
12:09 PM EDT on May 25, 2008
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1625. StormJunkie
4:09 PM GMT on May 25, 2008
lol nash.

Ok y'all I am off to enjoy the day and Pimp My Site to the local boating community !~)

See everyone later.
Member Since: August 17, 2005 Posts: 26 Comments: 16348
1624. KEEPEROFTHEGATE (Mod)
12:06 PM EDT on May 25, 2008
its not a ban
Member Since: July 15, 2006 Posts: 170 Comments: 53553
1623. nash28
4:06 PM GMT on May 25, 2008
Not sure SJ. I don't think anyone could, but who knows. I spent that time seething over Admin:-)
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1622. all4hurricanes
4:06 PM GMT on May 25, 2008
there are storms forming in the west pacific. The first one due east of Taiwan looks like a weak tropical storm but they're not gonna name it. the other one is about 10 degrees north, and east of the Philippians this should get it's name in time
probably Typhoon Enteng

why don't we watch the other ocean storms as much I think they're just as exciting
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1621. StormJunkie
4:05 PM GMT on May 25, 2008
Would not surprise me nash, just not sure if folks could still post in any of your blogs while you were banned?
Member Since: August 17, 2005 Posts: 26 Comments: 16348
1620. StormJunkie
4:03 PM GMT on May 25, 2008
Shen, I don't think he is banned, think he just has a blog without a title and therefore everything reverts to his previous blog??? I think, but maybe it is a ban...
Member Since: August 17, 2005 Posts: 26 Comments: 16348
1619. nash28
4:03 PM GMT on May 25, 2008
From the looks of it, Admin banned him. Probably 24hr ban.
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1618. ShenValleyFlyFish
3:54 PM GMT on May 25, 2008
1600. nash28

Its weird if you click on "Vort" you get sent to his archive and if you click on "comments" on last blog you wind up at today's stuff. Didn't try posting
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1617. nash28
4:01 PM GMT on May 25, 2008
They were SJ. Detroit is a puck possession team. I expect the Penguins to make adjustments and be a different team tomorrow night.
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1616. StormJunkie
3:59 PM GMT on May 25, 2008
Morning nash :~)

You talked me in to watching my first hockey game in quite some time last night. Good stuff. Was glad to see the Wings win. It was a very lopsided game though. Even though it was nil nil after the 1st, the Wings were just all over them.
Member Since: August 17, 2005 Posts: 26 Comments: 16348
1615. nash28
3:59 PM GMT on May 25, 2008
Doing well Chaser! Just getting my morning dose of wake up juice and morning dose of y'all:-) I've actually been up since 7:30, but still dragging. Need to get out and cut the front yard. Did the back yesterday. Heat and humidity damn near dropped me to my knees.
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1614. Stormchaser2007
11:58 AM EDT on May 25, 2008
Hey Nash, How are you?
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1613. nash28
3:58 PM GMT on May 25, 2008
Howdy SJ!
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1612. nash28
3:57 PM GMT on May 25, 2008
Why is Hank Williams Jr. running through my head???

"Are you ready for some tropics?"
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1611. StormJunkie
3:57 PM GMT on May 25, 2008
Welcome blip :~)


Amazing pics, sorry about the price that was paid for them.
Member Since: August 17, 2005 Posts: 26 Comments: 16348
1610. nash28
3:57 PM GMT on May 25, 2008
Morning Chaser, Keeper.
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1609. KEEPEROFTHEGATE (Mod)
11:51 AM EDT on May 25, 2008
theres a nice area of converging s boc off yuc with a strong rtn flow up over texas west gom lookin to see if dev occurs over the water there temps are 29 c in that zone convection appears to be building with a couple of cells just popin off shore of the nw yuc se boc
Member Since: July 15, 2006 Posts: 170 Comments: 53553
1608. Stormchaser2007
11:55 AM EDT on May 25, 2008
Yeah some stuff went down last night but we dont need to go into further detail.
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1607. nash28
3:55 PM GMT on May 25, 2008
I see the ridge is forecast to be somewhat of a blocking mechanism.
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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